What's the JPEG compression level?

When you save a file as jpeg you usually get an option to choose the compression or quality level. To know which level to choose you have one single reliable source: your own experience.

I did some experiments with a 2 Megabyte tiff file and measured the size when exported from different applications. The sizes varied widely between each application. Note that the only thing that can be measured absolutely is the file size - not the file quality. Quality can vary even more. The test was done with one single file. Other files may show very different behaviour.

Aperture and Photoshop have a scale from 0 to 12. An Aperture 12 jpeg was bigger than Photoshop 12. On the other hand, Aperture 0 was smaller than Photoshop 0, so Aperture's spread was wider.

Photoshop has a "Save for web..." option that increases the compatibility of the files. Here, the scale confusingly goes from 0 to 100. Both of those values are smaller than the corresponding files that result from "Save as..." in Photoshop with the settings 0 and 12.

Capture NX also goes from 0 to 100. It's 0 value is unusable, but Photoshop's 0 quality files, which are smaller, might work in some low requirement circumstances.

The gimp also goes from 0 to 100. It's 0 value quality looks like a bad computer game for a character based DOS program from the 1980ies, but it also is the smallest of them all.

All high quality jpegs look decent of course.

Numbers

Highest quality jpegs in each application: Aperture (1.1 M), Preview (1.1 M), Photoshop (912 k), Photoshop saved for web (780 k), Capture NX (712 k), gimp (644 k).

Lowest quality jpegs in each application: gimp (12 k), Photoshop saved for web (48 k), Capture NX (60 k), Preview (72 k), Aperture (76 k), Photoshop (88 k).

Lowest quality jpeg in Photoshop

Lowest quality jpeg in the gimp